Catheter systems are becoming an increasingly common way of diagnosing and treating abnormal heart conditions, in particular, heart arrhythmias. Such arrhythmias can be treated with drugs or by use of electronic devices such as pacemakers. However, these treatments alleviate, rather than cure, the condition.
In contrast, the use of ablative techniques has been shown to cure arrhythmias. Thus, catheters having mapping electrodes and/or ablative electrodes are inserted through the vascular system of a patient's body so that a distal end of the catheter can be placed accurately in the relevant chamber of the heart. For the treatment of atrial fibrillation, the distal end is placed at or around the ostium of one or more of the pulmonary veins, in turn, to effect ablation.
In still other applications of ablative catheters, the catheter may be placed against a wall of a blood vessel or organ, for example, for heating tumors to treat such tumors. It is, therefore, desirable that a distal end of the catheter be substantially planar so that the distal end of the catheter assembly can be placed in contact with the wall of the vessel or organ.
A catheter assembly is disclosed in U.S. Pat. No. 6,771,996 (“the '996 patent”). This catheter assembly includes an outer catheter having a lumen and an inner catheter sized to fit within and slide through the lumen of the outer catheter. Both catheters may be introduced into an anatomical site through a single introduction path. At the distal end region of each catheter is an electrode system. One electrode system is for mapping the site; the other is for ablating the site. The distal end regions of the catheters are able to assume a predetermined coiled or radially expanded configuration in the absence of an external force. During introduction of the inner and outer catheters into the anatomical site, a guide wire extends through the catheters to deform the catheters from their naturally coiled or expanded configuration into a constrained linear configuration. Alternatively, a cylindrical introducer is placed over the catheters to constrain the catheters. Once the distal ends of the catheters have been placed at the desired anatomical location, the guide wire or introducer is removed to allow the catheters to assume their predetermined coiled or radially expanded configurations.
A disadvantage of each of the catheter system embodiments disclosed in the '996 patent is that the inner and outer catheters assume a specific, predetermined configuration after insertion. Accordingly, the shape of the catheters cannot be adjusted after insertion to account for differences in anatomical geometries. Therefore, a large variety of differently configured catheters must be provided to cater for these differing geometries. Moreover, the time taken to complete a procedure on a patient can be significantly increased if the initially inserted catheter system needs to be swapped with a differently configured catheter system during the procedure. This additional time means that the patient, and in some cases the physician, has longer exposure to radiation or drugs required during the procedure.
A further disadvantage of the catheter system embodiments disclosed in the '996 patent is that the inner catheter extends through an opening in the sidewall of the outer catheter. It can be difficult to align the distal end of the inner catheter with the sidewall opening in the outer catheter. The sidewall opening also complicates manufacture of the outer catheter and represents a location of potential weakness in the outer catheter.